Background Multiple breakouts may present challenges during catheter ablation of ventricular arrhythmias (VAs, premature ventricular contractions, PVCs and/or nonsustained ventricular tachycardia, NSVT) arising from the right ventricular outflow tract septum (RVOT).
Objective The purpose of this study was to clarify the breakout sites and origin site and investigate their electrophysiological characteristics in idiopathic VAs arising from the RVOT.
Methods Nine patients occurred second PVCs with a different morphology after ablation of target PVCs were studied. Electroanatomical mapping (EAM) was performed in RVOT during sinus rhythm. Intracardiac electrograms of successful ablation site were evaluated by local activation time (LAT) and pace mapping (PM). Electroanatomical voltage mapping (EVM) was analysed after procedure.
Results In all patients, target PVCs had narrower QRS duration than the second one (P = 0.001), the successful target site (Ts) had later LAT and worse template-matching (TM) score than the target site (Tt) of target PVCs which determined by LAT and PM (P < 0.000, P = 0.030, respectively), and the stimulus to QRS interval was slightly longer during pacing at target than EVA site (P = 0.053). The distance between the Ts site and Tt site was 19 ± 8 mm and the target site always located at the transitional-voltage zone (TVZ, 0.5–1.5mV).
Conclusions RVOT-VAs often shows multiple or deformation of QRS morphologies caused by multiple breakouts and a single origin, which may be explained by anisotropic conduction of the TVZ resulting from the complex histology characteristics of the RVOT.